The
Loch Ness Monster, Bigfoot, The Lizard Man, flying saucers, and diamond tools that last
forever. What do all of these things have in common? They do not exist! Sure you have
heard stories about them, but have you ever actually seem them? The funny thing is that
the more experts investigate the facts about each of these phenomena, the more
they agree that they do not exist. But, when it comes to diamond wheels for flat glass
fabrication, many people involved with the sale or usage of diamond tools simply do not
know the facts.

This article will attempt to dispel some false information
and will specifically focus on resin bonded cup wheels. It will also attempt to answer a
variety of questions. Why is a resin matrix used in the manufacturing of glass grinding
wheels? How many different types of resins are used? What differentiates the wheels from
each other? How can you be sure you are getting the best tool for your application? I will
explore each of these questions and perhaps dispel some myths about diamond tools. We will
leave the other myths for someone else to explain.

Resin as a Bond Matrix

The reason resin is used as a bond matrix is simple: manufacturers need a compound
that will hold small diamond crystals and release these as they become dull. When metal is
used as a matrix, ultra fine diamond crystals cannot be used. Additionally, when a metal
matrix and small diamond crystals are used together the diamonds are not released when
dulled. As a result, the metal will glaze or smear the metal
matrix over the face of the wheel. The closed face of the wheel damages the glass surface
making it impossible to polish the surface to an acceptable finish. The closed face also
creates heat, which will eventually destroy the wheel as heat is a destroyer of diamond.
The type of resin used for cup wheel manufacturing is a simple catalyst driven, plant
derived substance that is activated (set) by heat. Melamine and phenolic resins, as they
are called, are formed into shape by applying a combination of pressures and temperatures
over a predetermined time. The resin matrix, in powder form, is mixed with the required
diamond crystal size (grit or mesh), poured into a mold, and set using heat and pressure.
The resin powder and diamond crystals change to a liquid because of the heat. The pressure
then forms the powder into the shape of the mold, and a cooling period completes the
process. The wheel then is removed from the mold and precision machined to fit the
required glass grinding machinery. The problem with this type of resin is after it is
transformed from solid-liquid-solid, the compounds new form continually evaporates.
This result gives resin products a finite shelf life. The amount of shelf life is the
basis for argument, but this continual drying process will affect the
performance of this type of tool. The amount of time the tool can be inventoried and not
begin to have an adverse affect on the performance is approximately three
years.

Super Secret Resin?

Is there a super secret resin? No. All resin wheels are manufactured basically the
same and have the same basic characteristics. There is no super resin used and, in fact,
there is no need for one: the diamond crystals determine the life of the tool. Super
resins could be used, but if the diamond crystals are held too long there is no advantage
gained. Diamond grains held too long by the resins or prematurely dulled by the grinding
operation will cause a glazing on the wheel face. The resin face will actually
melt preventing new diamonds from being exposed. Resin wheels sharpen themselves by
continually releasing old dull diamond crystals and new sharp diamonds are exposed. When
resin wheels must be dressed manually, use a very fine aluminum oxide stick (approximately
325 grit) or a pumice stone. Normally resin wheels will self dress as explained above, but
it is not uncommon for them to need manual dressing. If you are dressing your resin wheels
continually, contact your supplier because something is wrong.

Fillers and Porosity

Fillers are added to the resin compound to aid in lubricity. Graphite and Cerium
Oxide are the two main types of fillers, but additional fillers are added in an effort to
strengthen the resin. Resins have the natural physical property of being very brittle,
thus fillers are added to give the resin a certain resiliency and to avoid breakage. These
fillers aid in holding the diamond grain by enabling the resin to absorb the vibrations
created during the grinding process and not fracture. Unlike when grinding metals, the
grinding process of glass is not a cutting action, but a chipping action. The glass does
not slice, the removal of glass is a controlled breaking process.

Porosity is added to resin bonded diamond wheels in an effort to reduce the surface
contact of the wheels. Porosity is created by adding salt to the resin bond compound prior
to the actual pressing process. During the pressing process the salt evaporates and leaves
the holes (or porosity) in the bond. Slotted or turbo style resins accomplish the same
results. Slotted or turbo wheels are manufactured by replacing the normally smooth mold
tops with a mold top containing teeth. The teeth are pressed into
the resin compound leaving the slots in the bond. Problems sometimes found with these
methods of bond softening are the pores or slots can become clogged with the
grinding slurry and actually scratch the glass. Properly-engineered bonds do not need the
added porosity or slots to grind efficiently.

Diamonds

Diamonds used in resin wheels are all man-made. While there are many manufacturers
of diamond grit, there are only two major manufacturers of man-made diamondsDeBeers
and General Electric. These two manufacturers use state-of-the-art processes to
manufacture, then separate grit and grain sizes.

The perfect diamond for glass fabrication has a slightly higher degree of roughness and
is not too smooth and blocky. The diamond crystals must be friable (able to fracture and
stay sharp) but not fracture prematurely. Several diamond wheel manufacturers have
experimented with different styles of diamond grits, including those coated with various
compounds, such as nickel, copper, and titanium, in an effort to increase the life of
diamond grain. But, in the end the cost prohibits most of these processes and success of
these programs has been, at best, questionable. This leaves most wheel manufacturers using
basically the same diamond powders from these two vendors.

Super Resin Wheels

So, where do the resin wheels capable of running three to five million inches come
from? Clearly they do not exist. The average life of all resin wheels being sold today is
between 400,000 inches up to a maximum of 1,500,000 inches. This is not to say some users
cant get more inches, but it is highly unlikely that in a production atmosphere
these higher numbers could be maintained. Strangely enough, the actual expense of the
resin wheels when compared to the amount of inches of glass produced is also much lower
than most people realize. For example, a resin wheel that costs $145 and produces one
million inches of beveled glass costs .000145 cents to the customer. A resin wheel that
costs $145 and produces three million inches of beveled glass costs .000048 cents to the
customer. Clearly, this is not the area where customers will find huge savings. The ease
of polish, scrap-rate, grindabilty, and reputation of your vendor are much more important
factors. Does your supplier work with your operators? Train your personnel on how to get
the most from your tools and machines? When purchasing diamond tools, be careful not to
exclude these areas as they can cause large losses or profits to your company.

So, how should an end user decide which resin wheel is best? How quickly a wheel can be
set on the machine and begin to produce quality glass should be a major factor. The only
time your machine is not making you money is when it is not running! The amount of
scrapped metal produced by the wheels is also lost revenue and should be considered.
Quality of sales representation should also be a consideration. Do you trust your sales
staff to keep you updated on new products and proper usage of current products? Now, if we
could only train Bigfoot and the Lizard Man to run good glass.

Decisions, Decisions

Deciding Which Resin Wheel to Buy

 Choose wheels easy to set-up and use.
 Choose wheels that produce a minimum of scrap.
 Buy from a supplier you trust.
 Use wheels consistent in quality.
 Choose wheels first and negotiate price second.
 Choose a supplier large enough to provide support if problems do occur.
 Follow manufacturers instructions when testing new products and test in full
sets when possible.

Rick Haynes serves as diamond tools sales manager for Salem
Distributing Company located in Clemmons, NC.